error[E0698]: type inside `async` object must be known in this context
  --> $DIR/async-error-span.rs:12:9
   |
LL |     let a;
   |         ^ cannot infer type
   |
note: the type is part of the `async` object because of this `await`
  --> $DIR/async-error-span.rs:13:5
   |
LL |     get_future().await;
   |     ^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0698`.